1. Field of the Invention
The invention relates generally to sampling systems and more particularly to parallel processing architectures for sampling and digitizing high frequency input signals.
2. Description of the Prior Art
Digital Storage Oscilloscopes (DSOs) and Waveform Digitizers (WFDs) are increasingly being utilized in many complex fields, such as, for example, digital electronics and memory systems, general purpose design work, automated test and production systems, communications, radar and nuclear engineering.
The particular features of DSOs and WFDs that make them so useful in these fields are:
1. Single-shot capture of transient electronic events.
2. Pre-trigger Recording which captures data prior to the leading edge of an observed electronic event.
3. Digital Storage which provides the possibility for post-acquisition data processing and long term data storage of important electronic events.
4. Enhanced Accuracy for both amplitude and time measurements.
5. Post Acquisition Data Processing which allows the user to perform Fourier transforms, averages, and other calculations for state-of-the-art measurements.
6. Digital Interface in the form of an IEEE-488 bus, or other standard buses, which facilitates complete talk/listen capability with external control or data processing systems.
7. Automatic Self-Calibration for guaranteed accuracy.
8. Automatic Set-Up of sensitivity and time base parameters provides for an exceptionally friendly human interface.
9. Built-in Diagnostics provide a self test capability to enhance trouble shooting and repair procedures.
DSOs and WFDs work by rapidly sampling, at precise intervals, a succession of instantaneous voltage levels along the input waveform to be captured. These levels are ultimately converted into a corresponding stream of binary numbers, typically, of 6 bits or more and stored in a digital memory. At this point the memory will contain an exact numerical replica of the original input waveform and is subject to additional processing, display, output or erasure.
Even though the DSOs and WFDs are the only known means of providing this impressive set of capabilities, they, surprisingly, have not yet found their way onto every laboratory bench. The reason is simple. Presently available analog to digital conversion systems are too slow and too inaccurate. Existing analog to digital conversion systems have maximum sample rates of only 100 MHz to 200 MHz, except for scan converters which are discussed later.
Most of the known conversion schemes can be fit into one of three categories:
a. Direct analog to digital conversion. PA1 b. Scan conversion. PA1 c. Fast-in slow-out conversion.